For use in vehicles such as automobiles, rear wheel toe angle control systems are known that include an electric actuator connected between a vehicle body part and a wheel side member such as a knuckle, a hub carrier or the like of each rear wheel, and retracted and extended as required to variably adjust the toe angle of the corresponding rear wheel. See patent documents 1 and 2.
The rear wheel toe angle control system variably adjusts the toe angle of each rear wheel according to the steering condition of the front wheels and/or the running and operating conditions of the vehicle with the aim of improving the cornering performance and motion stability of the vehicle.
The electric actuator used for such a rear wheel toe angle control system typically consists of an electric motor and a feed screw mechanism. The rotational output of the electric motor is converted into a linear motion output by the feed screw mechanism.
When a vehicle equipped with a rear wheel toe angle control system using an electric actuator is operated under extreme conditions that may occur in motor racings, or that may be caused by incessant steering actions, because the rear wheel toe angle is changed frequently so as to correspond to the operating condition of the vehicle (front wheel steering condition), the load of the electric motor increases, and this causes the temperature of the brushes of the electric motor to rise. The rise in the temperature of the brushes may damage the performance and/or component parts of the electric motor, and may increase the possibility of the failure of the electric motor.
It may be possible to alleviate this problem by having the controller of the toe angle control system perform a protective logic in which the brush temperature of the electric motor is estimated from the motor electric current or detected by using a temperature sensor, and upon detection of a rise of the brush temperature to a prescribed motor protection temperature, after gradually returning the toe angle to zero, the operation of the electric motor is stopped. Once the brush temperature falls below the motor protection temperature, the normal toe angle control may be resumed. The toe angle is gradually returned to zero when the brush temperature has risen to the motor protection temperature because the vehicle may behave in an undesirable manner if the toe angle is quickly returned to zero.